Apoptotic cell suicide is a fundamentally important biological process that is required to maintain the integrity and homeostasis of multicellular organisms. Inappropriate apoptosis, however, underlies the etiology of many of the most intractable of human diseases. In only the last few years, many of the molecules that participate in a conserved biochemical pathway that mediates the highly ordered process of apoptotic cell suicide have been identified. At the heart of this pathway are a family of cysteine proteases, the xe2x80x98caspasesxe2x80x99, that are related to mammalian interleukin-1xcex2 converting enzyme (ICE/caspase-1) and to CED-3, the product of a gene that is necessary for apoptotic suicide in the nematode C. elegans (Nicholson et al., 1997, Trends Biochem Sci 22:299-306). The role of these proteases in cell suicide is to disable critical homeostatic and repair processes as well as to cleave key structural components, resulting in the systematic and orderly disassembly of the dying cell.
The central importance of caspases in these processes has been demonstrated with both macromolecular and peptide-based inhibitors (which prevent apoptosis from occurring in vitro and in vivo) as well as by genetic approaches. Inhibition of apoptosis via attenuation of caspase activity should therefore be useful in the treatment of human diseases where inappropriate apoptosis is prominent or contributes to disease pathogenesis. Caspase inhibitors would thus be useful for the treatment of human diseases including, but not limited to, acute disorders such as cardiac and cerebral ischemia/reperfusion injury (e.g. stroke), spinal cord injury and organ damage during transplantation, as well as chronic disorders such as neurodegenerative diseases (e.g. Alzheimer""s, polyglutamine-repeat disorders, Down""s, spinal muscular atrophy, multiple sclerosis), immunodeficiency (e.g. HIV), diabetes, alopecia and aging.
Ten caspases have so far been identified in human cells. Each is synthesized as a catalytically dormant proenzyme containing an amino-terminal prodomain followed by the large and small subunits of the heterodimeric active enzyme. The subunits are excised from the proenzyme by cleavage at Asp-X junctions (Nicholson et al., 1997, Trends Biochem Sci 22:299-306). The strict requirement by caspases for Asp in the P1 position of substrates is consistent with a mechanism whereby proenzyme maturation can be either autocatalytic or performed by other caspases. The three dimensional crystal structures of mature caspase-1 and -3 show that the large subunit contains the principle components of the catalytic machinery, including the active site Cys residue which is harbored within the conserved pentapeptide motif, QACxG,1 and residues that stabilize the oxyanion of the tetrahedral transition state (Wilson et al., 1994, Nature 370:270-75; Walker et al., 1994, Cell 78:342-52; Rotonda et al., 1996, Nat Struct Biol 3:619-25). Both subunits contribute residues which stabilize the P1 Asp of substrates while the small subunit appears to contain most of the determinants that dictate substrate specificity and, in particular, those which form the specificity-determining S4 subsite. One distinctive feature of these proteases is the absolute requirement for an aspartic acid residue in the substrate P1 position. The carboxylate side chain of the substrate P1 Asp is tethered by four residues in caspase-1 (Arg179, Gln238 from p20 and Arg341, Ser347 from p10) that are absolutely conserved in all caspase family members. Catalysis involves a typical cysteine protease mechanism involving a catalytic dyad, composed of His237 and Cys285 (contained within an absolutely conserved QACxG pentapeptide) and an xe2x80x98oxyanion holexe2x80x99 involving Gly238 and Cys285. Inhibitors bind, however, in an unexpected non-transition state configuration (which raises important considerations for inhibitor design) with the oxyanion of the thiohemiacetal being stabilized by the active site His237.
Members of the caspase family can be divided into three functional subgroups based on their substrate specificities which have been defined by a positional-scanning combinatorial substrate approach. The principle effectors of apoptosis (group II caspases, which include caspases-2, -3 and -7 as well as C. elegans CED-3) have specificity for [P4]DExD[P1], a motif found at the cleavage site of most proteins known to be cleaved during apoptosis. On the other hand, the specificity of group III caspases (caspases-6, -8, -9 and -10, as well as CTL-derived granzyme B) is [P4](I,V,L)ExD[P1] which corresponds to the activation site at the junction between the large and small subunits of other caspase proenzymes including group II (effector) family members. This and other evidence indicates that group III caspases function as upstream activators of group II caspases in a proteolytic cascade that amplifies the death signal. The role of group I caspases (caspases-1, -4 and -5) appears to be to mediate cytokine maturation and their role in apoptosis, if any, has not been substantiated.
A tetrapeptide corresponding to the substrate P4-P1 residues is sufficient for specific recognition by caspases and as a consequence has formed the basis for inhibitor design. In addition to the requirement for a P1 Asp, the P4 residue in particular appears to be most important for substrate recognition and specificity. Caspase-1, for example, prefers a hydrophobic residue such as Tyr in P4 (which corresponds to its YVHD cleavage site within proIL-1xcex2) whereas caspase-3 (and other group II enzymes) has a preference for an anionic Asp residue (which corresponds to the DXXD cleavage sites within most polypeptides that are cleaved by these enzymes during apoptosis). Peptide aldehydes, nitriles and ketones are potent reversible inhibitors of these proteases while compounds that form thiomethylketone adducts with the active site cysteine (e.g. peptide (acyloxy)methylketones) are potent irreversible inhibitors. For example, the tetrapeptide aldehyde Ac-YVAD-CHO (SEQ ID NO: 24) (which was designed to mimic the YVHD caspase-1 recognition sequence within proIL-1xcex2) is a potent inhibitor of caspase-1 (Ki less than 1 nM) but a poor inhibitor of caspase-3 (Ki=12 xcexcM) (Thornberry et al., 1992, Nature 356:768-74). In contrast, the Ac-DEVD-CHO (SEQ ID NO: 25) tetrapeptide aldehyde (which was designed to mimic the caspase-3 recognition site) is a very potent inhibitor of caspase-3 (Ki less than 1 nM) although it is also a weaker but reasonable inhibitor of caspase-1, presumably owing to promiscuity in the S4 subsite of this enzyme (Nicholson et al., 1995, Nature 376:37-43).
Several features plague these peptide-derived inhibitors as a platform for drug design. In addition to their metabolic instability and membrane impermeability, the slow-binding time-dependent inhibition of activity (e.g. kon caspase-1:Ac-YVAD-CHO (SEQ ID NO: 24)=3.8xc3x97105 Mxe2x88x921sxe2x88x921; kon caspase-3:Ac-DEVD-CHO (SEQ ID NO: 25)=1.3xc3x97105 Mxe2x88x921sxe2x88x921) precludes them from the rapid inhibition characteristics that may be necessary to abolish enzymatic activity in vivo. The present patent application describes the resolution of this issue with the discovery of several novel ketones that make highly suitable caspase inhibitors.
The invention encompasses the novel class of compounds represented by formula I: 
or a pharmaceutically acceptable salt thereof, wherein:
R is selected from the group consisting of:
(a) H and
(b) C(O)R1;
R1 is selected from the group consisting of:
(a) hydrogen,
(b) C1-6alkoxy,
(c) NR6R7,
(d) benzyloxy or mono- or disubstituted benzyloxy, wherein the substituent is selected from the group consisting of:
(1) methyl,
(2) halogen,
(3) methoxy and
(4) cyano,
(e) C1-6alkyl or substituted C1-6alkyl, wherein the substituent is selected from the group consisting of:
(1) hydroxy,
(2) halo,
(3) C1-3alkoxy,
(4) C1-3alkylthio,
(5) phenyl C1-3alkoxy,
(6) phenyl C1-3alkylthio,
(7) phenylcarboxy and
(8) carboxy,
(f) aryl or arylC1-6alkyl wherein the aryl group is selected from the group consisting of:
(1) phenyl,
(2) naphthyl,
(3) pyridyl,
(4) furyl,
(5) thienyl,
(6) thiazolyl,
(7) isothiazolyl,
(8) imidazolyl,
(9) benzimidazolyl,
(10) pyrazinyl,
(11) pyrimidyl,
(12) quinolyl,
(13) isoquinolyl,
(14) benzofuryl,
(15) benzothienyl,
(16) pyrazolyl,
(17) indolyl,
(18) purinyl,
(19) isoxazolyl and
(20) oxazolyl, and
(g) mono and di-substituted aryl as defined above in items (1) to (20) of (f), wherein the substituents are independently selected from:
(1) halo,
(2) amino,
(3) nitro,
(4) hydroxy,
(5) cyano,
(6) carboxy,
(7) formyl,
(8) amino carbonyl,
(9) C1-6alkyl,
(10) C1-6fluoroalkyl,
(11) C1-6alkylcarbonyl,
(12) C1-6alkoxycarbonyl,
(13) C1-6alkoxy,
(14) C1-6alkylthio,
(15) C1-6alkylsulfonyl and
(16) deuterio;
R2 is selected from the group consisting of:
(a) H,
(b) CH3,
(c) CH(CH3)2,
(d) CH2CH(CH3)2,
(e) CH2Ph,
(f) CH2PhOH,
(g) CH2OH,
(h) CH2SH,
(i) CH2CH2SCH3,
(j) CH(CH3)CH2CH3,
(k) CH(CH3)OH,
(l) CH2COOH,
(m) CH2CH2COOH,
(n) CH2CH2CH2NHCNH(NH2),
(o) CH2CH2CH2CH2NH2,
(p) CH2C(O)NH2,
(q) CH2CH2C(O)NH2,
(r) CH2CO2C1-4alkyl,
(s) CH2SC1-4alkyl,
(t) CH2S(O)2C1-4alkyl, 
or R2 and X2 together form a saturated monocyclic ring having the following structure: 
R3 is selected from the group consisting of:
(a) H,
(b) CH3,
(c) CH(CH3)2,
(d) CH2CH(CH3)2,
(e) CH2Ph,
(f) CH2PhOH,
(g) CH2OH,
(h) CH2SH,
(i) CH2CH2SCH3,
(j) CH(CH3)CH2CH3,
(k) CH(CH3)OH,
(l) CH2COOH,
(m) CH2CH2COOH,
(n) CH2CH2CH2NHCNH(NH2),
(o) CH2CH2CH2CH2NH2,
(p) CH2C(O)NH2,
(q) CH2CH2C(O)NH2,
(r) CH2CH2CO2C1-4alkyl,
(s) CH2CH2S(O)2C1-4alkyl, 
or R3 and X3 together form a saturated monocyclic ring having the following structure: 
R4 is selected from the group consisting of:
(a) H,
(b) CH3,
(c) CH(CH3)2,
(d) CH2CH(CH3)2,
(e) CH2Ph,
(f) CH2PhOH,
(g) CH2OH,
(h) CH2SH,
(i) CH2CH2SCH3,
(j) CH(CH3)CH2CH3,
(k) CH(CH3)OH,
(l) CH2COOH,
(m) CH2CH2COOH,
(n) CH2CH2CH2NHCNH(NH2),
(o) CH2CH2CH2CH2NH2,
(p) CH2C(O)NH2,
(q) CH2CH2C(O)NH2, 
or R4 and X4 together form a saturated monocyclic ring having the following structure: 
R5 is selected from the group consisting of:
(a) C1-6alkyl,
(b) arylC1-8alkyl wherein the aryl is selected from the group consisting of:
(1) phenyl,
(2) naphthyl,
(3) pyridyl,
(4) furyl,
(5) thienyl,
(6) thiazolyl,
(7) isothiazolyl,
(8) imidazolyl,
(9) benzimidazolyl,
(10) pyrazinyl,
(11) pyrimidyl,
(12) quinolyl,
(13) isoquinolyl,
(14) benzofuryl,
(15) benzothienyl,
(16) pyrazolyl,
(17) indolyl,
(18) purinyl,
(19) isoxazolyl,
(20) oxazolyl and
(21) coumarinyl and
(c) aryl as defined above in items (1) to (21) of (b), wherein the aryl portions may be optionally mono- or di-substituted with a substituent independently selected from:
(1) halo,
(2) amino,
(3) nitro,
(4) hydroxy,
(5) cyano,
(6) carboxy,
(7) formyl,
(8) amino carbonyl,
(9) C1-6alkyl,
(10) C1-6fluoroalkyl,
(11) C1-6alkylcarbonyl,
(12) C1-6alkoxycarbonyl,
(13) C1-6alkoxy,
(14) C1-6alkylthio and
(15) C1-6alkylsulfonyl;
R6 and R7 are independently selected from the group consisting of:
(a) C1-4alkyl,
(b) C1-4fluoroalkyl and
(c) benzyl or mono- or disubstituted benzyl wherein the substituent is selected from the group consisting of:
(1) methyl,
(2) halogen,
(3) methoxy and
(4) cyano,
or R6 and R7 may be joined to form a pyrrolidine, piperidine, morpholine, thiamorpholine or Nxe2x80x94R8 substituted piperazine wherein R8 is H or C1-3alkyl; and
X2, X3 and X4 are independently H or X2 and R2, X3 and R3, or X4 and R4 may together form a saturated monocyclic ring having the following structure: 
The invention also encompasses a pharmaceutical composition comprising a compound of formula I in combination with a pharmacuetically acceptable carrier.
The invention also encompasses a method of treating cardiac and cerebral ischemia/reperfusion injury (e.g. stroke), type I diabetes, immune deficiency syndrome (including AIDS), cerebral and spinal cord trauma injury, organ damage during transplantation, alopecia, aging, Parkinson""s disease, Alzheimer""s disease, Down""s syndrome, spinal muscular atrophy, multiple sclerosis and neurodegenerative disorders, comprising administering to a mammalian patient in need of such treatment an effective amount of a compound of formula I.
The invention encompasses the novel class of compounds represented by formula I, which are caspase-3 inhibitors. 
or a pharmaceutically acceptable salt thereof, are disclosed, wherein:
R is selected from the group consisting of:
(a) H and
(b) C(O)R1;
R1 is selected from the group consisting of:
(a) hydrogen,
(b) C1-6alkoxy,
(c) NR6R7,
(d) benzyloxy or mono- or disubstituted benzyloxy, wherein the substituent is selected from the group consisting of:
(1) methyl,
(2) halogen,
(3) methoxy and
(4) cyano,
(e) C1-6alkyl or substituted C1-6alkyl, wherein the substituent is selected from the group consisting of:
(1) hydroxy,
(2) halo,
(3) C1-3alkoxy,
(4) C1-3alkylthio,
(5) phenyl C1-3alkoxy,
(6) phenyl C1-3alkylthio,
(7) phenylcarboxy and
(8) carboxy,
(f) aryl or arylC1-6alkyl wherein the aryl group is selected from the group consisting of:
(1) phenyl,
(2) naphthyl,
(3) pyridyl,
(4) furyl,
(5) thienyl,
(6) thiazolyl,
(7) isothiazolyl,
(8) imidazolyl,
(9) benzimidazolyl,
(10) pyrazinyl,
(11) pyrimidyl,
(12) quinolyl,
(13) isoquinolyl,
(14) benzofuryl,
(15) benzothienyl,
(16) pyrazolyl,
(17) indolyl,
(18) purinyl,
(19) isoxazolyl and
(20) oxazolyl, and
(g) mono and di-substituted aryl as defined above in items (1) to (20) of (f), wherein the substituents are independently selected from:
(1) halo,
(2) amino,
(3) nitro,
(4) hydroxy,
(5) cyano,
(6) carboxy,
(7) formyl,
(8) amino carbonyl,
(9) C1-6alkyl,
(10) C1-6fluoroalkyl,
(11) C1-6alkylcarbonyl,
(12) C1-6alkoxycarbonyl,
(13) C1-6alkoxy,
(14) C1-6alkylthio,
(15) C1-6alkylsulfonyl and
(16) deuterio;
R2 is selected from the group consisting of:
(a) H,
(b) CH3,
(c) CH(CH3)2,
(d) CH2CH(CH3)2,
(e) CH2Ph,
(f) CH2PhOH,
(g) CH2OH,
(h) CH2SH,
(i) CH2CH2SCH3,
(j) CH(CH3)CH2CH3,
(k) CH(CH3)OH,
(l) CH2COOH,
(m) CH2CH2COOH,
(n) CH2CH2CH2NHCNH(NH2),
(o) CH2CH2CH2CH2NH2,
(p) CH2C(O)NH2,
(q) CH2CH2C(O)NH2,
(r) CH2CO2C1-4alkyl,
(s) CH2SC1-4alkyl,
(t) CH2S(O)2C1-4alkyl, 
or R2 and X2 together form a saturated monocyclic ring having the following structure: 
R3 is selected from the group consisting of:
(a) H,
(b) CH3,
(c) CH(CH3)2,
(d) CH2CH(CH3)2,
(e) CH2Ph,
(f) CH2PhOH,
(g) CH2OH,
(h) CH2SH,
(i) CH2CH2SCH3,
(j) CH(CH3)CH2CH3,
(k) CH(CH3)OH,
(l) CH2COOH,
(m) CH2CH2COOH,
(n) CH2CH2CH2NHCNH(NH2),
(o) CH2CH2CH2CH2NH2,
(p) CH2C(O)NH2,
(q) CH2CH2C(O)NH2,
(r) CH2CH2CO2C1-4alkyl,
(s) CH2CH2S(O)2C1-4alkyl, 
or R3 and X3 together form a saturated monocyclic ring having the following structure: 
R4 is selected from the group consisting of:
(a) H,
(b) CH3,
(c) CH(CH3)2,
(d) CH2CH(CH3)2,
(e) CH2Ph,
(f) CH2PhOH,
(g) CH2OH,
(h) CH2SH,
(i) CH2CH2SCH3, 
(j) CH(CH3)CH2CH3,
(k) CH(CH3)OH,
(l) CH2COOH,
(m) CH2CH2COOH,
(n) CH2CH2CH2NHCNH(NH2),
(o) CH2CH2CH2CH2NH2,
(p) CH2C(O)NH2,
(q) CH2CH2C(O)NH2, 
or R4 and X4 together form a saturated monocyclic ring having the following structure: 
R5 is selected from the group consisting of:
(a) C1-6alkyl,
(b) arylC1-8alkyl wherein the aryl is selected from the group consisting of:
(1) phenyl,
(2) naphthyl,
(3) pyridyl,
(4) furyl,
(5) thienyl,
(6) thiazolyl,
(7) isothiazolyl,
(8) imidazolyl,
(9) benzimidazolyl,
(10) pyrazinyl,
(11) pyrimidyl,
(12) quinolyl,
(13) isoquinolyl,
(14) benzofuryl,
(15) benzothienyl,
(16) pyrazolyl,
(17) indolyl,
(18) purinyl,
(19) isoxazolyl,
(20) oxazolyl and
(21) coumarinyl, and
(c) aryl as defined above in items (1) to (21) of (b), wherein the aryl portions may be optionally mono- or di-substituted with a substituent independently selected from:
(1) halo,
(2) amino,
(3) nitro,
(4) hydroxy,
(5) cyano,
(6) carboxy,
(7) formyl,
(8) amino carbonyl,
(9) C1-6alkyl,
(10) C1-6fluoroalkyl,
(11) C1-6alkylcarbonyl,
(12) C1-6alkoxycarbonyl,
(13) C1-6alkoxy,
(14) C1-6alkylthio and
(15) C1-6alkylsulfonyl;
R6 and R7 are independently selected from the group consisting of:
(a) C1-4alkyl,
(b) C1-4fluoroalkyl and
(c) benzyl or mono- or disubstituted benzyl wherein the substituent is selected from the group consisting of:
(1) methyl,
(2) halogen,
(3) methoxy and
(4) cyano,
or R6 and R7 may be joined to form a pyrrolidine, piperidine, morpholine, thiamorpholine or Nxe2x80x94R8 substituted piperazine wherein R8 is H or C1-3alkyl; and
X2, X3 and X4 are independently H or X2 and R2, X3 and R3, or X4 and R4 may together form a saturated monocyclic ring having the following structure: 
In a preferred embodiment, the compounds are represented by formula Ia 
or a pharmaceutically acceptable salt thereof, wherein the amino acids from which the structure is constructed, represented in formula Ia as AA1, AA2 and AA3, are selected from a group consisting of the L- and D-forms of the amino acids including alanine, arginine, asparagine, aspartic acid, cysteine, glutamine, glutamic acid, glycine, histidine, isoleucine, leucine, lysine, methionine, phenylalanine, proline, serine, threonine, tryptophane, tyrosine and valine. The structures of the L-amino acids are shown below. 
A preferred embodiment of the invention is that wherein R1 is C1-6alkyl or phenyl.
Another preferred embodiment of the invention is that wherein R5 is arylC1-8alkyl, wherein aryl is selected from the group consisting of phenyl, naphthyl, pyridyl, and mono-, or di-substituted derivatives thereof, wherein the substituents are individually selected from the group consisting of:
(1) halo,
(2) amino,
(3) nitro,
(4) hydroxy,
(5) cyano,
(6) carboxy,
(7) formyl,
(8) amino carbonyl,
(9) C1-3alkyl,
(10) C1-3fluoroalkyl,
(11) C1-3alkylcarbonyl,
(12) C1-3alkoxycarbonyl,
(13) C1-3alkoxy,
(14) C1-3alkylthio and
(15) C1-3alkylsulfonyl;
Another preferred embodiment of the present invention is that wherein:
R1 is selected from the group consisting of:
(a) C1-6alkoxy,
(b) benzyloxy or mono- or disubstituted benzyloxy, wherein the substituent is selected from methyl, halogen, methoxy and cyano,
(c) C1-6alkyl or substituted C1-6alkyl, wherein the substituent is selected from the group consisting of:
(1) hydroxy,
(2) halo,
(3) C1-3alkoxy,
(4) C1-3alkylthio,
(5) phenylC1-3alkoxy,
(6) phenylC1-3alkylthio,
(7) phenylcarboxy and
(8) carboxy,
(d) aryl or arylC1-6alkyl wherein the aryl group is selected from the group consisting of:
(1) phenyland
(2) naphthyl, and
(e) mono and di-substituted aryl as defined above in items (1) to (2) wherein the substituents are independently selected from:
(1) halo,
(2) hydroxy,
(3) cyano,
(4) carboxy,
(5) amino carbonyl,
(6) C1-3alkyl,
(7) C1-3fluoroalkyl,
(8) C1-3alkylcarbonyl,
(9) C1-3alkoxycarbonyl,
(10) C1-3alkoxy,
(11) C1-3alkylthio,
(12) C1-3alkylsulfonyl and
(13) deuterio; and
R5 is arylC1-8alkyl wherein aryl is selected from the group consisting of phenyl, naphthyl, pyridyl, and mono-, or di-substituted derivatives thereof, wherein the substituents are individually selected from the group consisting of:
(1) halo,
(2) hydroxy,
(3) cyano,
(4) carboxy,
(5) amino carbonyl,
(6) C1-3alkyl,
(7) C1-3fluoroalkyl,
(8) C1-3alkylcarbonyl,
(9) C1-3alkoxycarbonyl,
(10) C1-3alkoxy,
(11) C1-3alkylthio and
(12) C1-3alkylsulfonyl.
Another preferred embodiment of the invention is that wherein R1 is selected from the group consisting of:
(a) C1-6alkyl or substituted C1-6alkyl, wherein the substituent is selected from the group consisting of:
(1) hydroxy,
(2) halo,
(3) C1-3alkoxy,
(4) C1-3alkylthio,
(5) phenylC1-3alkoxy,
(6) phenylC1-3alkylthio,
(7) phenylcarboxy and
(8) carboxy,
(b) aryl or arylC1-6alkyl wherein the aryl group is selected from the group consisting of:
(1) phenyl and
(2) naphthyl, and
(c) mono and di-substituted aryl as defined above in items (1) to (2) wherein the substituents are independently selected from:
(1) halo,
(2) hydroxy,
(3) cyano,
(4) carboxy,
(5) amino carbonyl,
(6) C1-3alkyl,
(7) C1-3fluoroalkyl,
(8) C1-3alkylcarbonyl,
(9) C1-3alkoxycarbonyl,
(10) C1-3alkoxy,
(11) C1-3alkylthio,
(12) C1-3alkylsulfonyl and
(13) deuterio.
Another preferred embodiment of the present invention is that wherein R2 is selected from the group consisting of:
(a) CH2CO2H,
(b) CH2CO2C1-4alkyl,
(c) CH2SC1-4alkyl and
(d) CH2S(O)2C1-4alkyl.
Another preferred embodiment of the invention is that wherein R3 is selected from the group consisting of:
(a) CH3,
(b) CH2CH2CO2H,
(c) CH2CH2CO2C1-4alkyl,
(d) CH2CH2S(O)2C1-4alkyl.
A preferred embodiment of the present invention is that wherein R4 is isopropyl.
Another preferred embodiment of the invention is that wherein R5 is selected from the group consisting of:
(a) C1-6alkyl,
(b) arylC1-8alkyl wherein the aryl is selected from the group consisting of:
(1) phenyl,
(2) naphthyl,
(3) pyridyl and
(4) coumarinyl, and
(c) aryl as defined above in items (1) to (4) of (b), wherein the aryl portions may be optionally mono- or di-substituted with a substituent independently selected from:
(1) halo,
(2) hydroxy,
(3) cyano,
(4) carboxy,
(5) amino carbonyl,
(6) C1-3alkyl,
(7) C1-3fluoroalkyl,
(8) C1-3alkylcarbonyl,
(9) C1-3alkoxycarbonyl,
(10) C1-3alkoxy,
(11) C1-3alkylthio and
(12) C1-3alkylsulfonyl.
In one subset that is of particular interest, the compounds are represented by formula II: 
including pharmaceutically acceptable salts thereof, wherein:
R5 is selected from the group consisting of:
(a) C1-6alkyl,
(b) arylC1-8alkyl wherein the aryl is selected from the group consisting of:
(1) phenyl,
(2) naphthyl,
(3) pyridyl and
(4) coumarinyl and
(c) aryl as defined above in items (1) to (4) of (b), wherein the aryl portions may be optionally mono- or di-substituted with a substituent independently selected from:
(1) halo,
(2) hydroxy,
(3) cyano,
(4) carboxy,
(5) amino carbonyl,
(6) C1-3alkyl,
(7) C1-3fluoroalkyl,
(8) C1-3alkylcarbonyl,
(9) C1-3alkoxycarbonyl,
(10) C1-3alkoxy,
(11) C1-3alkylthio and
(12) C1-3alkylsulfonyl.
(13)
Another subset of compounds that is of particular interest relates to compounds of formula II wherein:
R5 is selected from the group consisting of:
(a) methyl,
(b) propyl,
(c) phenyl,
(d) phenylC1-5alkyl,
(e) 4-methoxyphenylpropyl,
(f) napthylpropyl and
(g) 4-methylcoumarinyl.
(h)
Representative compounds that are of particular interest are the following: 
In another embodiment that is of particular interest, the compounds are represented by formula III: 
including pharmaceutically acceptable salts thereof, wherein:
R1 is selected from the group consisting of:
(a) C1-6alkyl or substituted C1-6alkyl, wherein the substituent is selected from the group consisting of:
(1) hydroxy,
(2) halo,
(3) C1-3alkoxy,
(4) C1-3alkylthio,
(5) phenylC1-3alkoxy,
(6) phenylC1-3alkylthio,
(7) phenylcarboxy and
(8) carboxy,
(b) aryl or arylC1-6alkyl wherein the aryl group is selected from the group consisting of:
(1) phenyl and
(2) naphthyl, and
(c) mono and di-substituted aryl as defined above in items (1) to (2) wherein the substituents are independently selected from:
(1) halo,
(2) hydroxy,
(3) cyano,
(4) carboxy,
(5) amino carbonyl,
(6) C1-3alkyl,
(7) C1-3fluoroalkyl,
(8) C1-3alkylcarbonyl,
(9) C1-3alkoxycarbonyl,
(10) C1-3alkoxy,
(11) C1-3alkylthio,
(12) C1-3alkylsulfonyl and
(13) deuterio; and
R5 is arylC1-8alkyl wherein aryl is selected from the group consisting of phenyl, naphthyl, pyridyl, and mono-, or di-substituted derivatives thereof, wherein the substituents are individually selected from the group consisting of:
(1) halo,
(2) hydroxy,
(3) cyano,
(4) carboxy,
(5) amino carbonyl,
(6) C1-3alkyl,
(7) C1-3fluoroalkyl,
(8) C1-3alkylcarbonyl,
(9) C1-3alkoxycarbonyl,
(10) C1-3alkoxy,
(11) C1-3alkylthio and
(12) C1-3alkylsulfonyl.
A subset of compounds that are of particular interest are defined in accordance with formula III wherein:
R1 is selected from the group consisting of:
(a) methyl,
(b) phenyl and
(c) mono- or disubstituted phenyl, wherein the substituents are selected from the group consisting of:
(1) halo and
(2) deuterio; and
R5 is arylC3-5alkyl wherein aryl is selected from the group consisting of phenyl and naphthyl.
Representative compounds that are of particular interest are the following: 
Yet another embodiment that is of particular interest is represented by formula IV: 
including pharmaceutically acceptable salts thereof, wherein:
R9 is selected from the group consisting of:
(a) CO2H,
(b) CO2C1-4alkyl,
(c) SC1-4alkyl and
(d) S(O)2C1-4alkyl;
R10 is selected from the group consisting of:
(a) H,
(b) CH2CO2H,
(c) CH2CO2C1-4alkyl,
(d) CH2S(O)2C1-4alkyl; and
Ar is selected from the group consisting of:
(a) phenyl and
(b) napthyl.
A subset of compounds that are of particular interest are defined in accordance with formula IV wherein:
R9 is selected from the group consisting of:
(a) CO2H,
(b) SCH3 and
(c) S(O)2CH3;
R10 is selected from the group consisting of:
(a) H and
(d) CH2S(O)2CH3; and
Ar is phenyl or napthyl.
Representative compounds that are of particular interest are the following: 
In a preferred embodiment, the invention encompasses a method of treating a caspase-3 mediated disease in a mammalian patient in need of such treatment, comprising administering to said patient a compound of formula I in an amount effective to treat said caspase-3 mediated disease.
In another embodiment, the invention encompasses a method of treating cardiac and cerebral ischemia/reperfusion injury (e.g. stroke), type I diabetes, immune deficiency syndrome (including AIDS), cerebral and spinal cord trauma injury, organ damage during transplantation, alopecia, aging, Parkinson""s disease, Alzheimer""s disease, Down""s syndrome, spinal muscular atrophy, multiple sclerosis and neurodegenerative disorders, comprising administering to a mammalian patient in need of such treatment an effective amount of a compound of formula I.
In another embodiment, the invention encompasses a method of treating acute disorders, including cardiac and cerebral ischemia/reperfusion injury (e.g. stroke), spinal cord injury and organ damage during transplantation, in a mammalian patient in need of such treatment, comprising administering to said patient a compound of formula I in an amount effective to treat said acute disorder.
In another embodiment, the invention encompasses a method of treating chronic disorders, including neurodegenerative diseases (e.g. Alzheimer""s, polyglutamine-repeat disorders, Down""s, spinal muscular atrophy, multiple sclerosis), immunodeficiency (e.g. HIV), diabetes, alopecia and aging, in a mammalian patient in need of such treatment, comprising administering to said patient a compound of formula I in an amount effective to treat said chronic disorder.
In another embodiment, the invention encompasses a method of treating a caspase-3 mediated disease in a mammalian patient in need of such treatment, comprising administering to said patient a compound of formula II in an amount effective to treat said caspase-3 mediated disease.
In another embodiment, the invention encompasses a method of treating a caspase-3 mediated disease in a mammalian patient in need of such treatment, comprising administering to said patient a compound of formula III in an amount effective to treat said caspase-3 mediated disease.
In another embodiment, the invention encompasses a method of treating a caspase-3 mediated disease in a mammalian patient in need of such treatment, comprising administering to said patient a compound of formula IV in an amount effective to treat said caspase-3 mediated disease.
For purposes of this specification, the following abbreviations have the indicated meanings:
For purposes of this specification alkyl means linear, branched or cyclic structures and combinations thereof, containing one to twenty carbon atoms. Examples of alkyl groups include methyl, ethyl, propyl, isopropyl, butyl, s- and t-butyl, pentyl, hexyl, heptyl, octyl, nonyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, eicosyl, 3,7-diethyl-2,2-dimethyl-4-propylnonyl, cyclopropyl, cyclopentyl, cycloheptyl, adamantyl, cyclododecylmethyl, 2-ethyl-1-bicyclo[4.4.0]decyl and the like.
Alkylcarbonyl signifies groups having the formula xe2x80x94C(O)xe2x80x94 alkyl, wherein alkyl is defined as above.
Alkylsulfonyl signifies groups having the formula xe2x80x94S(O)2xe2x80x94 alkyl, wherein alkyl is defined as above.
For purposes of this specification fluoroalkyl means linear, branched or cyclic alkyl groups and combinations thereof, of one to ten carbon atoms, in which one or more hydrogen but no more than six is replaced by fluorine. Examples are xe2x80x94CF3, xe2x80x94CH2CH2F, and xe2x80x94CH2CF3, and the like.
Alkoxy means alkoxy groups of one to ten carbon atoms of a straight, branched or cyclic configuration. Examples of alkoxy groups include methoxy, ethoxy, propoxy, isopropoxy, and the like.
Alkoxycarbonyl signifies groups having the formula xe2x80x94C(O)xe2x80x94 alkoxy, wherein alkoxy is defined as above.
Alkylthio means alkylthio groups of one to ten carbon atoms of a straight, branched or cyclic configuration. Examples of alkylthio groups include methylthio, propylthio, isopropylthio, etc. By way of illustration, the propylthio group signifies xe2x80x94SCH2CH2CH3.
Aryl is, for example, phenyl, naphthyl, pyridyl, furyl, thienyl, thiazolyl, isothiazolyl, imidazolyl, benzimidazolyl, pyrazinyl, pyrimidyl, quinolyl, isoquinolyl, benzofuryl, benzothienyl, pyrazolyl, indolyl, purinyl, isoxazolyl, oxazolyl and coumarinyl.
Halo includes F, Cl, Br and I.
The compounds described typically contain asymmetric centers and may thus give rise to diastereomers and optical isomers. The present invention is meant to comprehend such possible diastereomers as well as their racemic and resolved, enantiomerically pure forms and pharmaceutically acceptable salts thereof.
Some of the compounds described herein contain olefinic double bonds, and unless specified otherwise, are meant to include both E and Z geometric isomers.
The pharmaceutical compositions of the present invention comprise a compound of formula I as an active ingredient or a pharmaceutically acceptable salt thereof in combination with a pharmaceutically acceptable carrier, and optionally other therapeutic ingredients. The term xe2x80x9cpharmaceutically acceptable saltsxe2x80x9d refers to salts prepared from pharmaceutically acceptable bases including inorganic bases and organic bases. Representative salts derived from inorganic bases include aluminum, ammonium, calcium, copper, ferric, ferrous, lithium, magnesium, manganic salts, manganous, ammonium, potassium, sodium, zinc and the like. Particularly preferred are the calcium, magnesium, potassium, and sodium salts. Representative salts derived from pharmaceutically acceptable organic bases include salts of primary, secondary and tertiary amines, substituted amines including naturally occurring substituted amines, cyclic amines, and basic ion exchange resins, such as arginine, betaine, caffeine, choline, N,Nxe2x80x2-dibenzylethylenediamine, diethylamine, 2-diethylaminoethanol, 2-dimethylaminoethanol, ethanolamine, ethylenediamine, N-ethyl-morpholine, N-ethylpiperidine, glucamine, glucosamine, histidine, hydrabamine, isopropylamine, lysine, methylglucamine, morpholine, piperazine, piperidine, polyamine resins, procaine, purines, theobromine, triethylamine, trimethylamine, tripropylamine, tromethamine and the like.
When the compound of the present invention is basic, salts may be prepared from pharmaceutically acceptable non-toxic acids, including inorganic and organic acids. Examples of such acids include acetic, benzenesulfonic, benzoic, camphorsulfonic, citric, ethanesulfonic, fumaric, gluconic, glutamic, hydrobromic, hydrochloric, isethionic, lactic, maleic, malic, mandelic, methanesulfonic, mucic, nitric, pamoic, pantothenic, phosphoric, succinic, sulfuric, tartaric, p-toluenesulfonic acid, and the like. Particularly preferred are citric, hydrobromic, hydrochloric, maleic, phosphoric, sulfuric and tartaric acids.
In the discussion of methods of treatment which follows, reference to the compounds of formula I are meant to also include the pharmaceutically acceptable salts.
The ability of the compounds of formula I to inhibit caspase-3 make them useful research tools in the field of apoptosis. These compounds are also useful to treat, prevent or ameliorate in mammals and especially in humans, diseases including but not limited to:
1. cardiac and cerebral ischemia/reperfusion injury (e.g. stroke)
2. type I diabetes
3. immune deficiency syndrome (including AIDS)
4. cerebral and spinal cord trauma injury
5. organ damage during transplantation
6. alopecia
7. aging
8. Parkinson""s disease
9. Alzheimer""s disease
10. Down""s syndrome
11. spinal muscular atrophy
12. multiple sclerosis
13. neurodegenerative disorders
The magnitude of therapeutic dose of a compound of formula I will, of course, vary with the nature of the severity of the condition to be treated and with the particular compound of formula I and its route of administration and vary upon the clinician""s judgement. It will also vary according to the age, weight and response of the individual patient. An effective dosage amount of the active component can thus be determined by the clinician after a consideration of all the criteria and using is best judgement on the patient""s behalf. A representative dose will range from 0.001 mpk/d to about 100 mpk/d.
An ophthalmic preparations for ocular administration comprising 0.001-1% by weight solutions or suspensions of the compounds of formula I in an acceptable ophthalmic formulation may be used.
Any suitable route of administration may be employed for providing an effective dosage of a compound of the present invention. For example, oral, parenteral and topical may be employed. Dosage forms include tablets, troches, dispersions, suspensions, solutions, capsules, creams, ointments, aerosols, and the like.
The compositions include compositions suitable for oral, parenteral and ocular (ophthalmic). They may be conveniently presented in unit dosage form and prepared by any of the methods well-known in the art of pharmacy.
In practical use, the compounds of formula I can be combined as the active ingredient in intimate admixture with a pharmaceutical carrier according to conventional pharmaceutical compounding techniques. The carrier may take a wide variety of forms depending on the form of preparation desired for administration. In preparing the compositions for oral dosage form, any of the usual pharmaceutical media may be employed, such as, for example, water, alcohols, oils, flavoring agents, preservatives, coloring agents and the like in the case of oral liquid preparations, such as, for example, suspensions, elixirs and solutions; or carriers such as starches, sugars, microcrystalline cellulose, diluents, granulating agents, lubricants, binders, disintegrating agents and the like in the case or oral solid preparations such as, for example, powders, capsules and tablets, with the solid oral preparations being preferred over the liquid preparations. Because of their ease of administration, tablets and capsules represent the most advantageous oral dosage unit form in which case solid pharmaceutical carriers are obviously employed. If desired, tablets may be coated by standard aqueous or nonaqueous techniques.
Pharmaceutical compositions of the present invention suitable for oral administration may be presented as discrete units such as capsules, cachets or tablets each containing a predetermined amound of the active ingredient, as a powder or granules or as a solution or a suspension in an aqueous liquid, a non-aqueous liquid, an oil-in-water emulsion or a water-in-oil emulsion. Such compositions may be prepared by any of the methods of pharmacy but all methods include the step of bringing into active ingredient with the carrier which constitutes one or more necessary ingredients. In general, the compositions are prepared by uniformLy and intimately admixing the active ingredient with liquid carriers or finely divided solid carriers or both, and then, if necessary, shaping the product into the desired presentation. For example, a tablet may be prepared by compression or molding, optionally with one or more accessory ingredients. Compressed tablets may be prepared by compressing in a suitable machine, the active ingredient in a free-flowing form such as powder or granules, optionally mixed with a binder, lubricant, inert diluent, surface active or dispersing agent. Molded tablets may be made by molding in a suitable machine, a mixture of the powdered compound moistened with an inert liquid diluent. For example, each dosage unit may contain from about 0.01 mg to about 1.0 g of the active ingredient.
Method of Synthesis
Compounds of the instant invention are conveniently prepared using the procedures described generally below and more explicitly described in the Example section thereafter. 
A mixed anhydride of N-protected-L-aspartic acid xcex2-tert-butyl ester (protected-L-Asp (OtBu)-OH)(V) and isobutylchloroformate (IBCF) is formed in the presence of N-methylmorpholine (NMM). This anhydride is reduced to the corresponding alcohol VI using sodium borohydride at xe2x88x9278xc2x0 C. The alcohol VI is then oxidized using dimethyl sulfoxide (DMSO), oxalyl chloride, and N,N-diisopropylethylamine to the corresponding aldehyde. The aldehyde (VII) is not isolated but reacted immediately with an organometallic reagent to afford the secondary alcohol (VIII) which can be oxidized to the corresponding ketone (IX). 
The ketones IX are loaded onto a solid support using the technology described by Webb et al. (J. Am. Chem. Soc. 114, 3156 (1992)). This method uses the solution synthesis of the complete semicarbazone carboxylic acid linker XI by first reacting ketone IX with semicarbazidyl-trans-4-methyl cyclohexanecarboxylic acid trifluoroacetate salt (X) to give XI. Coupling of XI to the commercially available Merrifield resin gives the insoluble support XII. This material has all the physical and chemical properties for the automated synthesis of peptides.
Toward this end the 9050 Plus PepSynthesizer from PerSeptive Biosystems is used (Millipore Corporation, 34 Maple Street, Milford, Mass. 01757, User""s Guide 9050 Plus OM 1.0). The synthesis procedure given in the user""s guide is followed for the preparation of the tetrapeptide XIII on solid support.
O-(7-Azabenzotriazol-l-yl)N,N,Nxe2x80x2,Nxe2x80x2-tetramethyluronium hexafluorophosphate (HATU) and N,N-diisoproylethylamine (DIEA) are used as coupling reagents instead of of TBTU and HOBt as described in the user""s guide.
The uncapped tetrapeptide XIII is acylated and peptide I can be obtained by simultaneous deesterification and cleavage from solid support via exposure to a 9:1 mixture of TFA:H2O.
The invention will now be illustrated by the following non-limiting examples in which, unless stated otherwise:
(i) all operations were carried out at room or ambient temperature, that is, at a temperature in the range 18-25xc2x0 C.,
(ii) evaporation of solvent was carried out using a rotary evaporator under reduced pressure (600-4000 pascals: 4.5-30 mm. Hg) with a bath temperature of up to 60xc2x0 C.,
(iii) the course of reactions was followed by thin layer chromatography (TLC) and reaction times are given for illustration only;
(iv) melting points are uncorrected and xe2x80x98dxe2x80x99 indicates decomposition; the melting points given are those obtained for the materials prepared as described; polymorphism may result in isolation of materials with different melting points in some preparations;
(v) the structure and purity of all final products were assured by at least one of the following techniques: TLC, mass spectrometry, nuclear magnetic resonance (NMR) spectrometry or microanalytical data;
(vi) yields are given for illustration only;
(vii) when given, NMR data is in the form of delta (xcex4) values for major diagnostic protons, given in parts per million (ppm) relative to tetramethylsilane (TMS) as internal standard, determined at 300 MHz or 400 MHz using the indicated solvent; conventional abbreviations used for signal shape are: s. singlet; d. doublet; t. triplet; m. multiplet; br. broad; etc.: in addition xe2x80x9cArxe2x80x9d signifies an aromatic signal;
(viii) chemical symbols have their usual meanings; the following abbreviations have also been used v (volume), w (weight), b.p. (boiling point), m.p. (melting point), L (litre(s)), mL (millilitres), g (gram(s)), mg (milligrams(s)), mol (moles), mmol (millimoles), eq (equivalent(s)).